1. Field of the Invention
This invention relates to heat exchanger evaporators and condensers, particularly those used in HVAC applications. The invention relates to a plate heat exchanger evaporator, where the refrigerant flows through the plates and evaporates, while a heat transfer fluid flows through adjacent plates and is cooled by the evaporating refrigerant. The invention also relates to a plate heat exchanger condenser. In a preferred embodiment, the evaporator is a component of a refrigeration system which can be used for cooling large quantities of water. This invention relates to an apparatus and method for increasing the heat transfer rate of these types of heat exchangers.
2. Description of the Related Art
Refrigeration systems of the type used to cool large quantities of water typically include a heat exchanger evaporator having separated passageways. One passageway carries refrigerant, and another carries the heat transfer fluid to be cooled, usually water. As the refrigerant travels through the evaporator, it absorbs heat from the heat transfer fluid and changes from a liquid to a vapor phase. After exiting the evaporator, the refrigerant proceeds to a compressor, then a condenser, then an expansion valve, and back to the evaporator, repeating the refrigeration cycle. The fluid to be cooled passes through the evaporator in separate fluid channels and is cooled by the evaporation of the refrigerant. The fluid can then be routed to a cooling system for cooling the spaces to be conditioned, or it can be used for other refrigeration purposes.
It is desirable to optimize the heat transfer rate between fluids flowing through sa heat exchanger, particularly large heat exchangers used in heating and air conditioning systems. A number of approaches have been proposed to improve the heat transfer characteristics of evaporators and condensers. One generally known approach is to create an electric field on a heat transfer surface in order to improve heat transfer. The use of an electric field to improve the heat transfer of convection heat transfer in a liquid is generally referred to as the electrohydrodynamic effect or EHD. Applications of this approach are disclosed in U.S. Pat. No. 4,651,806 to Allen et al., U.S. Pat. No. 5,072,780 to Yabe, and U.S. Pat. No. 5,769,155 to Ohadi et al.
The object of the present invention therefore is to provide improved heat exchanger methods and systems. Another object is to provide improved heat exchangers for HVAC applications that are more efficient and more compact than conventional heat exchangers.
The advantages and purposes of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. The advantages and purposes of the invention will be realized and attained by means of the elements and combinations particularly pointed out in the appended claims.
To attain the advantages and in accordance with the purposes of the invention, as embodied and broadly described herein, the invention includes a plate heat exchanger for accommodating a circulating refrigerant and heat transfer fluid. The plate heat exchanger includes a plurality of heat transfer plates and at least one electrode plate. The plurality of heat transfer plates are mounted in parallel relationship to each other defining alternating flow spaces for a refrigerant and a heat transfer fluid.
The electrode plate is located in each refrigerant flow space and is spaced from the adjacent heat transfer plates. The electrode plate includes outer electrode surfaces on each side thereof to produce an electric field. The effect of the electric field is an increase in the heat transfer rate between the refrigerant and heat transfer fluid. The plate heat exchanger typically includes a plurality of refrigerant flow spaces and corresponding electrode plates located therein.
In a further aspect of the invention, the invention includes a plate heat exchanger for accommodating two circulating heat exchange mediums. The plate heat exchanger includes a plurality of heat transfer plates and an electrode plate. The plurality of heat transfer plates are mounted in parallel relationship to each other to define alternating fluid channels comprising first and second fluid channels. The first fluid channel is for containing a first heat exchange medium, and the second fluid channel is for containing a second heat exchange medium. An electrode plate is located in each first fluid channel and is positioned generally parallel to and spaced from the heat transfer plates.
The electrode plate includes outer electrode surfaces on each side thereof to produce an electric field. Either the outer electrode surfaces of each electrode plate, or the surfaces of the heat transfer plates surrounding each electrode plate and defining the first fluid channel, include surface irregularities. The effect of the electric field on the surface irregularities is an increase in the heat transfer rate between the first heat exchange medium and the second heat exchange medium.
In a yet further aspect of the invention, the invention includes a method of exchanging heat between a heat transfer fluid and a refrigerant in a plate heat exchanger. In the method of the present invention, a plurality of parallel heat transfer plates are provided. An electrode plate is also provided inside each of a plurality of first flow spaces defined by first surfaces of adjacent heat transfer plates. Next, a refrigerant is flowed through the plurality of first flow spaces, and a heat transfer fluid is flowed along a second surface of each of the heat transfer plates. The second surfaces of adjacent heat transfer plates to define a second flow space for the heat transfer fluid. Lastly, a voltage is applied to the electrode plates to create an electric field, the electric field increasing the heat transfer rate between the refrigerant and the heat transfer fluid. The method may also include the step of forming surface irregularities on either the first surfaces of the heat transfer plates or on the surfaces of the electrode plates.
It is to be understood that both the foregoing general description and the following detailed description are exemplary and explanatory only and are not restrictive of the invention, as claimed.